1. Field of Invention
This invention relates generally to aviation instrumentation, and particularly to an indicating means for advising a pilot which of three entry procedures (direct, parallel, or tear drop) should be selected to enter a holding pattern.
2. Prior Art
The determination of the proper entry procedure ordinarily involves the pilot making mental calculations. With the increasing number of gauges, meters, signals, controls, and air traffic, the distractions from accurate mental calculations are vastly increased and the possibility of error is multiplied. In accordance with instrument flight rules, a pilot may be called to enter a holding pattern when air space is congested. The Federal Aviation Administration defines a holding pattern as
"A predetermined maneuver which keeps an aircraft within a specified air space - - - " PA1 (a) Parallel Procedure--Parallel holding course, turn left, and return to holding fix or intercept holding course. PA1 (b) Teardrop Procedure--Proceed on outbound track of 30.degree. (or less) to holding course, turn right to intercept holding course. PA1 (c) Direct Entry Procedure--Turn right and fly the pattern.
Entry into and flying a holding pattern requires flying (1) to the holding fix; (2) one of three predetermined entry procedures; (3) a first 180.degree. turn which places the aircraft on the outbound leg of the holding pattern; (4) the outbound leg; (5) a second 180.degree. turn which places the aircraft on the inbound leg of the holding pattern; (6) the inbound leg; (7) the pattern is repeated until the aircraft is released. This maneuver is continued until the conditions requiring the holding pattern no longer prevail and the pilot is authorized to proceed. The three holding pattern entry procedures are designated by the terms "direct", "parallel", and "tear drop". The Federal Aviation Administration issues the Airman's Information Manual particularly describing these procedures.
The following quotation is from the Airman's Information Manual:
(see exhibit attached to paper filed Mar. 27, 1978 from which the foregoing is quoted.)
The particular type of procedure pursued by the aircraft, can be either of the standard type, in which right hand turns are made in the pattern or the non-standard type in which left hand turns are made in the pattern. The pilot knows whether the holding pattern and entry will be standard or non-standard. The pilot determines the correct entry procedure according to the size of the angle determined by the angle between his immediate heading to the holding fix and the radial of the holding pattern at the holding fix. The Federal Aviation Administration defines a holding fix as "a specified fix as a reference point in establishing and maintaining the position of an aircraft while holding." It will be seen that in addition to the needs for observation and control of the aircraft, the pilot must mentally calculate this difference, and having made the calculation must select one of the three pre-determined entry procedures corresponding to that angle. This mental calculation is done by observing the aircraft's directional gyro, which is required by the Federal Aviation Administration to be installed on all aircraft operating on instrument flight rules. The directional gyroscope is an adaptation of the mariner's magnetic compass so constructed as not to be susceptible to turning errors or outside forces. The invention enables the pilot to make a determination by inspection of the gyro, without engaging in the mental exercise of arithmetical calculation that detracts from his attention to controls.